This invention relates to a satellite signature suppression shield for camouflaging a satellite's location from ground based and airborne tracking and detection systems. The purpose of the invention is to suppress the laser, radar, visible and infrared signatures of satellites to make it difficult or impossible for hostile enemy forces to damage or destroy satellites in orbit.
Several systems are known which are used to cripple or destroy orbiting satellites or other space vehicles. These systems may be ground based or space based. Typical systems used for destroying satellites include kinetic energy weapons delivered by anti-satellites; directed energy weapons such as high energy lasers, neutral particle beams, high-powered microwave radiation, and other nuclear radiations; and broad-area electromagnetic pulses. Before the satellite can be destroyed, however, it must be detected in space, and the weapon must be aimed such that the destructive force will intercept the path of the satellite. This invention relates to a device which makes it difficult or impossible to locate and track the satellite. When the word "satellite" is used in this specification, other space based mechanisms and vehicles are considered to be within the realm of the invention.
To destroy a satellite, the weapon operator must aim his weapon either to lead the satellite such that the energy beam (or the like) and target arrive at the same location at the same time, or the weapon must be able to track the satellite's location. Should the aim of the gunner be off, in the case of an unguided projectile, the gunner will miss the target. In the case of a guided projectile, the target position, velocity and acceleration information must be accurate enough to enable the projectile to come near enough to its target to be effective. If the input data is inaccurate or too late, the operator will not be able to make the appropriate corrective actions, and the weapon will miss.
Several factors influence the accuracy of the weapon and its ability to locate its target in outer space. Some factors make tracking satellites easier, and some factors make this more difficult. For example, ground based weapons are looking into outer space, i.e. into a non-reflective background. Oftentimes space based weapons systems are also looking out into the non-reflective background of outer space. This makes the tracking of the target easier, because there is no background radiation or other noise background in the sensor's view. The satellite, which is a radiation source and a radiation reflector, is very evident in this radiation-free background. When a tracking sensor is viewing a radiation scene from the air toward the earth's surface, it is more difficult to locate and track a satellite because of all of the background radiation from the earth and/or the objects below. Thus, it is easier for ground based weapon sensors, or sensors using outer space as a background, to track satellites.
Another factor which makes it easier to track satellites is the fact that once a satellite or other space object is in orbit, they follow very precise orbital tracks. Therefore, once a satellite's position is accurately determined and tracked, predictions of the future location of this satellite are very accurate. Some external forces, such as solar winds, do act on these satellites to alter their orbits; however, such orbital changes are typically small and gradual. Satellites are typically very limited in their maneuverability after they are in orbit. If they can be maneuvered at all, usually a very limited propulsion power supply is available, and there is no way to recharge the power supply. Hence, maneuvering is done infrequently and to a very limited extent. This makes satellites relatively easy to track. Airplanes, on the other hand, are continuously maneuverable because they have a readily available power supply. Thus, airplanes can continuously change directions to avoid ease in tracking and engagement with weapons.
There are other factors which make it more difficult to track and destroy satellites. One factor is the large distance between the ground based or space based attacker and the satellite. The attacker and target may be separated by hundreds of miles if the satellite is at relatively low altitudes, and even thousands of miles for higher altitudes. Therefore, the sensors being used must be highly directional and very powerful. Ground based sensors, in order to cover any significant area of space, must have many individual sensors which make up a large sensor device. These sensors cannot be proliferated in any way comparable to air defense sensors, and they are not easily moved. Therefore, the satellite launching party will know the location of the detecting sensors, and he will know when and where his satellite is detectable by the ground based sensor systems.
The large distance creates another problem when energy beams are employed as the weapon used for destruction. Because of this distance, in order for the energy beam to be effective when it reaches the target, extremely narrow beams must be used. The beam must reach the target with enough energy density to damage the target. This greatly complicates the aiming task, since the aiming must be very precise. Radar is not precise enough to aim the directed energy beams at great distances; very accurate closed loop laser or optical tracking systems must be used for aiming.
Another difficulty in tracking satellites results from the relative speeds of space objects. Not only are the targets difficult to locate, but they must be tracked for some significant time before the intercept is made. Low altitude objects are only in the sensor's field of view for a short time period; high altitude satellites require a long time period for the projectile to reach its target. The weapons used must have sufficient propulsion and acceleration energy to reach the location of the satellite. Any significant delay in dispatching the weapon may allow the satellite to exit the sensor's field of view before it can be tracked, or it may increase the separation distance such that the satellite is no longer within the weapon's range.
If the satellite signature or the energy required by the weapon tracking system is reduced or suppressed significantly, there may not be enough energy remaining for the weapon's tracking system to locate and track the target within the time period in which a successful attack may be launched. Reducing the available engagement time also enhances other satellite protection mechanisms, such as maneuverability, decoy deployment or other electronic counter measures.
The satellite signature is the characteristic pattern of radiation which is emitted by or reflected from the satellite. This signature enables remote based sensors to identify the object as a satellite. Various methods of reducing the signature radiation are known. For example, small dipole scatterers and absorbers have been used in camouflage shields to alter the radar signature of the satellite to make it appear like background. Other camouflage materials include special pigments which absorb radiation and re-radiate it at the proper wavelength so as to appear like chlorophyll to infrared sensors. Absorbing and non-reflecting materials have been used since World War II to reduce radar and sonar signatures on tactical aircraft and submarines, respectively. Curved surfaces and slanted configurations are also used to reduce well-defined edges at which radar (and sonar) reflection occurs. These configurations are currently used in the stealth bombers, and various other fighter and bomber aircraft.